This invention relates to part molding machines. More particularly, it relates to a system for monitoring the operational cycles of the machine to protect it from damage.
Part molding machines using a multiplicity of molding techniques such as injection molding are enjoying increasing popularity for making a wide variety of parts. One of the most expensive components of these machines is the molds which are of intricate design and particularly adapted to form the desired part. Typically, these molds are formed of two parts which are clamped together and filled with a liquid plastic whose configuration is defined by the mold. After the plastic is hardened, the molds are opened and the part is ejected from the molds.
One of the problems which is encountered in use of these part molding machines is that the molded part often is not fully ejected from the mold. Many of these machines are fully automated such that after a predetermined time the molds are automatically closed to begin another operational cycle. However, if a part or portion thereof has not cleared the mold, the hardened part can cause damage to the molds when they are again closed. Since it is imperative that the molds maintain their precise configuration, they cannot be reused, lest they form a deformed part, and must be repaired. This necessitates a large amount of down time, not to mention the repair of the relatively expensive molds.
Photoelectric devices have been used in the past to detect whether the parts have been ejected from the molds. Generally, a light beam is directed across the open faces of the molds and the transmitted light is monitored by a photocell. This arrangement has a variety of drawbacks. During ordinary machine usage, grease, oil, and other matter has a tendency to collect on the receiving face of the photocell thereby preventing proper operation. Moreover, the large amount of heat generated by the molds tend to degrade the solid state operational characteristics of the photocells. Furthermore, the photocell arrangements must be individually adapted to the shape of the molds where parts of different configurations are to be made. Since it is important to insure that the molds are completely free of hardened debris, relatively intricate photocell arrangements must be utilized to detect remnants of the part left in the mold.